HP 6104A Service manual

PRECISION POWER SUPPLIES
MODELS
61G4A, 6114A, 6105A,(6115A)
OPERATING AND SERVICE MANUAL
FOR SERIALS 1209A-00051 AND ABOVE *
*For Serials Above 1209A-00051 a change page may be included.
Hewlett-Packard
Part No. 5950-5976
Printed: June, 19 72

TABLE OF CONTENTS
Section Page
1 GENERAL INFORMATION.1-1
1-1 Description.1-1
1-4 Models 6104A and 6105A.-.. 1-1
1-10 Models 6114A and 6115A. 1 -1
1-16 Specifications. 1 -1
1-18 Options.. ... 1-3
1-20 Accessories.1-4
1-22 Instrument Identification.1-4
1- 25 Ordering Additional Manuals.1-4
2 INSTALLATION. 2 -1
2- 1 Initial Inspection...2-1
2-3 Mechanical Check..2-1
2-5 Electrical Check.. ..2-1
2-7 Repackaging for Shipment.2-1
2-9 Installation Data.... 2-1
2-11 Location ..2-1
2-13 Outline Diagram.2-1
2-15 Rack Mounting.2-1
2-17 Input Power Requirements...2-1
2- 20 Power Cable . ....2-2
3 OPERATING INSTRUCTIONS.-.3-1
3- 1 Turn-On Checkout Procedures . ...3-1
3-3 Operating Modes...3-2
3-5 Normal Operating Mode.3-2
3-8 Constant Voltage..3-2
3-10 Constant Current....3-3
3-12 Overvoltage Crowbar Operation.3-3
3-17 Connecting Load.3-4
3-21 Operation Beyond Normal Rated Output.. . 3-4
3-23 Remote Programming, Constant Voltage.3-4
3-29 Remote Programming, Constant Current.3-5
3-36 Remote Sensing (Figure 3-7) . . ■ ..3-6
3-41 Series Operation.3-7
3-43 Auto-Series Operation (Figure 3-9).3-7
3-47 Parallel Operation.3-8
3-49 Auto-Parallel Operation (Figure 3-11).3-8
3-52 Auto-Tracking Operation (Figure 3-12).3-9
3-55 Special Operating Considerations.3-9
3-56 Pulse Loading . ..3-9
3-58 Output Capacitance ..3-9
3-61 Reverse Voltage Loading.3-10
3-63 Reverse Current Loading.3-10
3-65 Gross Current Limit/Automatic Dual-Range Switching • . . .3-10
ii

1-1 DESCRIPTION
1-2 This instruction manual contains operating
and service instructions for four Hewlett-Packard
precision power supplies. The four models (desig¬
nated 6104A, 6105A, 6114A, and 6115A) are ideal
for applications requiring an accurate, highly stable,
and easily settable source of dc voltage or current.
All models are completely solid-state and feature
constant voltage/constant current operation, auto¬
matic dual-range operation, overvoltage crowbar
protection, front-panel voltage and current meter¬
ing, and provisions for remote voltage and current
programming. In addition, all models are capable
of auto-series, auto-parallel, and auto-tracking
operation. Front-panel mounted controls allow
current limit and overvoltage trip points to be con¬
veniently set, while OVERVOLTAGE and CURRENT
MODE light emitting diodes indicate when the cor¬
responding condition is in effect.
1-3 Additional features and characteristics appli¬
cable to specific models are described in the fol¬
lowing paragraphs. Section III of this manual cov¬
ers the use of all controls and indicators and gives
procedures for implementing the various operating
modes.
1-4 MODELS 6104A and 6105A
1-5 These models employ individual voltage and
current meters, and a 10-tum potentiometer for
setting output voltage levels. With the exception
of some component values and meter scale mark¬
ings, the two models are physically identical. For
improved settability, an optional three-digit deca-
dial voltage control (option 013) is available.
1-6 Model 6104A Output Ratings. The Model
6104A can be operated in either of two ranges: 0
to 20V at 0 to 2A; or 20 to 40V at 0 to 1A. Auto¬
matic voltage range crossover occurs if the load
current exceeds approximately 1A and the output
voltage has been set above 20V.
1-7 The front panel CURRENT control allows the
maximum output current to be set to any desired
value from 0 amps up to the maximum current rating
for the range. Using this control, the power supply
can be operated as a constant current source with
0.01% current regulation. The front panel CURRENT
MODE indicator lights when either the maximum
(gross) current limit is reached, or when the current
limit established by the front panel control is
reached. When the indicator is lighted, the output
voltage is uncalibrated. However, the front panel
voltmeter continues to indicate the output voltage
with an accuracy of 2%.
1-8 Model 61Q5A Output Ratings. The Model
6105A can be operated in either of two ranges:. 0
to 50V at 0 to 0. 8A; or 50 to 100V at 0 to 0. ^A.
Automatic voltage range crossover occurs if the
load current exceeds approximately 0. 4A and the
output voltage has been set above 50V.
1-9 The Model 6105A can also be used as a cur¬
rent source, as described in paragraph 1-7.
1-10 MODELS 6114A and 6115A
1-11 These models make use of a front-panel
mounted four-digit pushbutton control to increase
and decrease output voltage in unit steps. A
thumbwheel control is used to set the fifth (or
least significant) digit for output voltage accuracy
in the fractional millivolt range. A single meter,
combining both voltage and current functions, is
also located on the front panel. A METER slide
switch selects the function *o be indicated on the
meter. With the exception of component val¬
ues and meter scale markings, the 6114A and 6115A
are physically identical.
1-12 Model 6114A Output Ratings. The Model
6114A can be operated in either of two ranges: 0
to 20V at 0 to 2A; or 20 to 40V at 0 to 1A. Auto¬
matic voltage range crossover occurs if the load
current exceeds approximately 1A and the output
voltage has been set above 20V.
1-13 The Model 6114A can also be used as a cur¬
rent source, as described in paragraph 1-7.
1-14 Model 6115A Output Ratings. The Model
6115A can be operated in either of two ranges: 0
to 50V at 0 to 0, 8A; or 50 to 100V at 0 to 0.4A.
Automatic voltage range crossover occurs if the
load current exceeds approximately 0.4A and the
output voltage has been set above 50V.
1-15 The Model 6115A can also be used as a cur¬
rent source, as described in paragraph 1-7.
1-16 SPECIFICATIONS
1-17 Detailed specifications for all four models
are given in Table 1-1.
1-1

Table 1-1. Specifications, Models 6104A, 6105A, 6114A, 6115A
NOTE
Specifications apply to all models, unless
otherwise indicated.
GENERAL
INPUT POWER:
104-127 Vac, 48-440Hz, 15OVA maximum (Standard)
208-254 Vac, 48-440Hz, 150VA maximum (Switch
Selected)
DC OUTPUT:
Single output, dual range with automatic cross¬
over between ranges.
Models 6104A & 6114A: 0-20V, 2A/20-40V, 1A
Models 6105A & 6115A~: 0-50V, 0. 8A/50-100V,
0.4A
METERS:
Models 6104A and 61Q5A: Individual voltage and
current meters, with +2% full scale accuracy.
Models 6114A and 6115A: Single, dual-function
(voltage and current) meter, with ±2% full scale
accuracy.
TEMPERATURE RATINGS:
Operating: 0 to 55°C. Storage: -40 to + 75°C.
COOLING:
Convection cooling is employed. The supplies
have no moving parts.
DIMENSIONS:
See outline diagram. Figure 2-1.
WEIGHT:
17 lbs. (7, 7kg.) net. 21 lbs. (9,5kg.) shipping.
TEMPERATURE COEFFICIENT:
Output voltage change per degree Centigrade
change in ambient following 30-minute warm up.
Model 6104A: 0.005%+ 25p.V
Model 6105A: 0. 005% + 50uV
Model 6114A: 0.001%+ 15^V
Model 6115A; 0.001% + 15 |j.V
DRIFT:
Total voltage drift over 8-hour interval under
constant line, load, and ambient following a 30-
minute warm up. Conditions must be held con¬
stant during warm up.
Models 6104A & 6105A: 0.005%+ 50pV **
Models 6114A & 6115A: 0.0015%+ 15pV *
TRANSIENT RECOVERY TIME;
Less than 50|isec is required for output voltage
recovery to within lOmV of the nominal output
•voltage following a change in output current
equal to the current rating of the supply.
OUTPUT IMPEDANCE (typical):
Equivalent to a , 05mn. resistor in series with a
3 pH inductor,
RESOLUTION:
Minimum output voltage change obtainable using
front panel voltage controls.
Model 6104A: 8mV Model 6114A : 200pV
Model 6105A : 16mV Model 6115A : 200pV
OUTPUT VOLTAGE ACCURACY:
0.025%+ lmV, at 23°C±3°C, at any line vol. and
load cur. within rating, after 5-min, warm up.
REMOTE RESISTANCE PROGRAMMING:
2000n/V ± 0.01% Programming Coefficient.
CONSTANT VOLTAGE OUTPUT
LOAD REGULATION:
For load current change equal to current rating
of supply (measured at rear terminals).
Models 6I04A & 6114A: 0.0005%+ 100pV
Models 6105A & 6115A: 0.0005%+ 50pV
LINE REGULATION:
For a ±10% change in line voltage from nominal
value (115 Vac or 230 Vac),
Models 6104A & 6114A: 0.0005%+ 40pV
Models 6105A & 6115A: 0. 0005% + 100pV
RIPPLE AND NOISE:
40pVrms/l00|j.V p-p (up to 20MHz) at any line
voltage and under any load condition within rating
REMOTE VOLTAGE PROGRAMMING:
Programming Coefficient: 1V/V
Programming Accuracy: Accuracy of remote
source, ± 0. 2mV
REMOTE PROGRAMMING SPEED:
The maximum time required to non-repetitively
program from 0V to within 99. 9% of the maximum
rated output voltage (up programming), or from
the maximum rated output voltage to within 0. 1%
of that voltage above 0V (down programming).
61Q4A/6114A
up
prog.
down
prog.
'60msec (no load
,30msec (full load)
600msec (no load)
.30msec (full load)
6105A/6115A
150msec (no load)
75msec (full load)
1. 5sec (no load)
75msec (full load)

Table 1-1. Specifications, Models 6104A, 6105A, 6114A, 6115A (continued)
OVERVOLTAGE CROWBAR PROTECTION:
Trip Voltage Range (approximate): 0. 5V to 10%
above rated output voltage of supply.
Margin: Minimum 2% + 0.5V above output volt¬
age to prevent false activation.
DC OUTPUT ISOLATION:
Supply may be floated at up to 300V above
ground.
CONSTANT CURRENT OUTPUT
LOAD REGULATION:
0.01% + 500pA for load voltage change equal
to the voltage rating of the supply.
LINE REGULATION:
For a ±10% change in line voltage from nominal
value (115 Vac or 230 Vac).
Models 6104A & 6114A: 0.005%+ 40 ( xA
Models 6105A & 6115A; 0. 005%+ 20pA
RIPPLE AND NOISE:
200pA rms/lmA p-p at any line voltage and
under any load condition within rating.
TEMPERATURE COEFFICIENT:
Output change per degree Centigrade change in
ambient following 30~minute warm up.
Models 6104A & 6114A: 0. 02% + 50pA
Models 6105A & 6115A: 0.02%+ 25pA
DRIFT:
Total current drift in output over 8-hour interval
under constant line, load, and ambient following
30-minute warm up. Conditions must be held
constant during warm up.
Models 6104A & 6114A: 0.25% + 7mA * **
Models 6105A & 6II5A: 0.25% + 4mA *
RESOLUTION:
Minimum output current change obtainable using
front panel current control.
Models 6104A & 6114A: 15mA
Models 6105A & 6115A: 8mA
REMOTE RESISTANCE PROGRAMMING:
Models 6104A & 6114A: 500VA ± 0. 5%
Models 6105A & 6115A: 1000 a/A ± 0. 25%
REMOTE VOLTAGE PROGRAMMING:
Models 6104A & 6114A: 0. 5V/A ± 1%
Models 6105A & 6115A: 1V/A ± 1%
* Specified with final decade potentiometer set to zero. If potentiometer is set to value other
than zero thermally induced resistance shifts may cause drift of 0. 0015% + 200pV.
** Potentiometer wiper jump effect may add 5mV (6104A) or lOmV (6105A). When remote program¬
med, drift is 0.001% + 15pV plus stability of remote programming device.
^ When remote programmed, drift is 0.25% + 500pA plus stability of remote programming device.
1-18 OPTIONS
1-19 Options are customer-requested factory mod¬
ifications of a standard instrument. All of the op¬
tions described below apply to Models 6104A and
6105A. All except option 013 apply to Models 6114A
and 6115A.
Option No. Description
008 Ten-turn Output Current-Control:
Replaces standard single-turn cur¬
rent control to allow greater resol¬
ution in setting the output current
of supply.
013 Three Digit Graduated Decadial Vol¬
tage Control:
Replaces standard 10-tum voltage
control of Models 6104A and 6105A
for improved output voltage settabil-
ity.
Option No. Description
014 Three Digit Graduated Decadial Cur ¬
rent Control:
Includes 10-tum control, replacing
standard single-turn current control
for greater resolution in setting the
output current of supply.
040 Interfacing for Multiprogrammer Oper ¬
ation:
Prepares standard HP power supplies
for resistance programming by the
6940A Multiprogrammer or 6941A
Multiprogrammer Extender. Operation
with either of these instruments re¬
quires that the powe r supply be sub¬
jected to (1) Special Calibration, and
(2) Protection Checkout. The former
procedure insures that the power sup¬
ply can be accurately set to zero and

the maximum rated output voltage
or current when programmed by the
Multiprogrammer; the latter pro¬
cedure insures that the power sup¬
ply will not be damaged by the
rapid, repetitive programming pos¬
sible with the Multiprogrammer.
1-21 The accessories listed in the following chart
may be ordered with the instrument or separately
from your local Hewlett-Packard sales office (refer
to list at rear of manual for addresses).
HP Part No. Description
5060-8762 Dual Rack Adapter: Kit for rack
mounting one or two supplies in
standard 19-inch rack.
5060-8760 Blank Panel: Filler panel to block
unused half of rack when mounting
only one supply.
1052A Combining Case for mounting one or
two units in standard 19'' rack.
5060-0789 Cooling kit for above combining case,
115Vac, 50-60HZ.
5060-0796 Cooling kit for above combining case,
230Vac, 50-60Hz.
1-22 INSTRUMENT IDENTIFICATION
1-23 Hewlett-Packard power supplies are identif¬
ied by a three-part serial number. The first part
is the power supply model number. The second
part is the serial number prefix, consisting of a
number-letter combination denoting the date of a
significant design change and the country of man¬
ufacture. The first two digits indicate the year
(12 = 1972, 13 = 1973, 20 = 1980, etc); the sec¬
ond two digits indicate the week (01 through 52);
and the letter "A", "G", " J", or "U" designates
the U.S. A. , West Germany, Japan, or the United
Kingdom, respectively, as the country of manufac¬
ture. The third part is the power supply serial
number; a different 5-digit sequential number is
assigned to each power supply, starting with 00101.
1-24 If the serial number prefix on your unit does
not agree with the prefix on the title page of this
manual, change sheets supplied with the manual
or manual backdating changes in Appendix A define
the differences between your instrument and the
instrument described by this manual.
1-26 One manual is shipped with each instrument.
Additional manuals may be purchased from your
local Hewlett-Packard field office (see list at rear
of this manual-for addresses). Specify the model
number, serial number prefix, and HP part number
shown on the title page.
1-4

SECTION H
INSTALLATION
24 INITIAL INSPECTION
2-2 Before shipment, this instrument was in¬
spected and found to be free of mechanical and
electrical defects. As soon as the instrument is
received, proceed as instructed in the following
paragraphs.
2-3 MECHANICAL CHECK.
2-4 If external damage to the shipping carton is
evident, ask the carrier's agent to be present
when the instrument is unpacked. Check the in¬
strument for external damage such as broken con¬
trols or connectors, and dents or scratches on the
panel surfaces. If the instrument is damaged, file
a claim with the carrier's agent and notify your
local Hewlett-Packard Sales and Service Office as
soon as possible (see list at rear of this manual
for addresses).
2-5 ELECTRICAL CHECK
2-6 Check the electrical performance of the in¬
strument as soon as possible after receipt. Sec¬
tion V of this manual contains performance check
procedures which will verify instrument operation
within the specifications stated in Table 1-1. This
check is also suitable for incoming quality control
inspection. Refer to the inside front cover of the
manual for the Certification and Warranty state¬
ments.
21 REPACKAGING FOR SHIPMENT
2-8 To insure safe shipment of the instrument, it
is recommended that the package designed for the
instrument be used. The original packaging mater¬
ial is reusable. If it is not available, contact
your local Hewlett-Packard field office to obtain
the materials. This office will also furnish the
address of the nearest service office to which the
instrument can be shipped. Be sure to attach a
tag to the instrument specifying the owner, model
number, full serial number, and service required,
or a brief description of the trouble.
2-9 INSTALLATION DATA
2-10 The instrument is shipped ready for bench
operation. It is necessary only to connect the in¬
strument to a source of power and it is ready for
operation.
2-11 LOCATION
2-12 This instrument is convection cooled. Suf¬
ficient space should be allotted so that a free flow
of cooling air can reach the top and rear of the in¬
strument when it is in operation. It should be used
in an area where the ambient temperature remains
between 0°C and +55°C.
2-13 OUTLINE DIAGRAM
2-14 Figure 2-1 illustrates the outline shape and
dimensions of Models 6104A, 6105A, 6114A, and
6115A.
Figure 2-1. Outline Diagram
2-15 RACK MOUNTING
2-16 The Model 6104A, 6105A, 6114A, and 611SA
power supplies may be rack mounted using either
the dual rack adapter kit or the combining case
(with appropriate cooling kit) described in para¬
graph 1-20. The necessary installation instruct¬
ions are provided with the accessories.
247 INPUT POWER REQUIREMENTS
2-18 Models 6104A, 6105A, 6114A, and 6115A may
be operated continuously from either a nominal 120
volt or 240 volt, 48-440Hz power source. A two-
position selector switch (f) located within the
a-c power module on the rear panel selects the
power source. Before connecting the instrument to

2-20 POWER CABLE
the power source, check that the selector switch
setting matches the nominal line voltage of the
source. If required, move the switch to the other
position. Note that the power cable must be re¬
moved, the plastic door on the power module must
be moved aside, the fuse extractor must be pulled
outward and the fuse must be removed in order to
gain access to the selector switch.
2-19 When the instrument leaves the factory,
the proper fuse is installed for 115 volt operation.
An envelope containing a fuse for 230 volt opera¬
tion is attached to the instrument. Make sure
that the correct fuse is installed if the position of
the slide switch is changed (2A for 115 volt opera¬
tion, and 1A for 230 volt operation).
2-21 To protect operating personnel, the National
Electrical Manufacturers' Association (NEMA) rec¬
ommends that the instrument panel and cabinet be
grounded. This instrument is equipped with a three
conductor power cable. The third conductor is the
ground conductor and when the cable is plugged in¬
to an appropriate receptacle, the instrument is
grounded. The offset pin on the power cable's three-
prong connector is the ground connection.
2-22 To preserve the protection feature when oper¬
ating the instrument from a two-contact outlet, use
a three-prong to two-prong adapter and connect the
green lead on the adapter to ground.

Figure 3-1. Operating Controls and Indicators
3-1 TURN-ON CHECKOUT PROCEDURES
3-2 The following checkout procedure describes
the use of the front panel controls and indicators
(Figure 3-1) for either the dual meter, ten-turn
VOLTAGE control supplies (the 6104A or 6105A)
or the single meter, pushbutton VOLTAGE control
supplies (the 6114A or 6115A). The checkout pro¬
cedures ensure that the power supply is operation¬
al.
a. For the 6114A/6115A, set meter switch
© to VOLTS (there is no meter switch on the
6104A or 6105A).
b. Rotate OVERVOLTAGE (crowbar) control
© (screwdriver adjust) fully clockwise; and ro¬
tate CURRENT control © to middle of range.
c. Set LINE switch © to ON and observe
that indicator © lights.
d. Adjust VOLTAGE control © through the
entire output voltage range as indicated on meter.
© Adjust output for desired operating voltage
NOTE
To increase the 6114A/6115A output vol¬
tage, depress the pushbutton switch a-
bove the associated digit. To decrease
the voltage, depress the pushbutton
switch below the associated digit. Fine
output voltage adjustment is provided by
the millivolt digit thumbwheel potentio¬
meter.

e. To ensure that the overvoltage crowbar
circuit is operational, rotate the OVERVOLTAGE con¬
trol counterclockwise until the supply crowbars.
Output voltage will fall to approximately one volt
and the OVERVOLTAGE and CURRENT MODE indica¬
tors ( (|) and (|) , respectively) will light.
/f. To deactivate the crowbar, return the
OVERVOLTAGE control to maximum clockwise posi¬
tion and turn off supply. Turn supply back on and
output voltage should again be value obtained in
step (d),
g. To checkout the constant current circuit,
first turn off supply. Short circuit front panel output
terminals (+ to -). On the 6114A or 6.115A supplies
set meter switch to AMPS. Turn on the supply;
CURRENT MODE indicator (?) comes on.
h. Adjust CURRENT control through the en¬
tire output current range as indicated on meter.
Adjust output for desired operating current.
i. Remove short and connect load to output
terminals. Note that for maximum load protection
by the crowbar, the Load should be connected to
the rear terminals.
NOTE
The power supply features automatic
dual-range operation. If operating
voltage and current are both set above
the mid-points of supply's voltage and
current ratings, the supply will gross
current limit if current attempts to ex¬
ceed one-half the maximum current
rating of the supply. If output current
increases further, the supply enters
the constant current mode in which
output voltage is reduced in order to
supply the desired current. The VOLT¬
AGE control setting, therefore, is
overridden. See paragraph 3-65 for
more details.
3-3 OPERATING MODES
3-4 The power supply is designed so that its
mode of operation can be selected by making strap¬
ping connections between particular terminals on
the terminal strips at the rear of the power supply.
The terminal designations are stenciled on the
power supply above their respective terminals. The
operator can ground either the positive or negative
terminal or operate the power supply up to 3 00Vdc
off ground (floating). The following paragraphs des¬
cribe the procedures for utilizing the various oper¬
ational capabilities of the power supply. A more
theoretical description concerning the operational
features of this supply is contained in Application
Note 90 and in various Tech. Letters. Copies of
these can be obtained from your local Hewlett-
Packard field office.
3-6 The power supply is normally shipped with its
rear terminal strapping connections arranged for
constant Voltage/Constant Current, local sensing,
local programming, single unit mode of operation.
This strapping pattern is illustrated in Figure 3-2.
3-7 The operator selects either a constant voltage
or a constant current output using the front panel
controls (for local programming, no strapping changes
are necessary). Each supply is rated for two voltage
and current ranges as follows:
Model
Low Range
High Range
Voltage
Current
Voltage
Current
6104A/61I4A
6105A/6115A
0-20V
0-50V
0-2A
0-. 8A
20- 40V
50-100V
0-1A
0-.4A
When the VOLTAGE and CURRENT settings are with¬
in the specified ranges, the constant voltage and
constant current modes of operation are selected as
described below. If, however, VOLTAGE and CUR¬
RENT settings are required that are outside of the
specified ranges for normal operation (for instance,
the 6104A is set for 30V and 1. 5A), the power sup¬
ply provides automatic dual-range switching if
output current attempts to exceed the low range cur¬
rent rating. As current is limited (to approximately
65% of the maximum, low range, rating at nominal
line voltage), the VOLTAGE setting is overridden
and output voltage is reduced to the low range
(approximately 65% of the maximum, high range,
voltage rating at nominal line voltage). The supply
next enters the constant current mode during which
output voltage is reduced in order to supply the de¬
sired current. Refer to paragraph 3-65 for more in¬
formation on how the supply operates to gross cur¬
rent limit and automatically switch ranges,
3-8 CONSTANT VOLTAGE
3-9 To select a constant voltage output, within
the normal range ratings of the supply, proceed as
follows;
. a. Remove load from output terminals; turn¬
on supply and adjust VOLTAGE control for desired

output voltage.
b. S hort output terminals and adjust CURRENT
control for maximum output current allowable (cur¬
rent limit) as determined by load conditions and
voltage range selected in step (a). If a load change
attempts to cause the output current to exceed this
setting, the power supply will automatically cross¬
over to constant current mode and output current
will be constant at the level set by the CURRENT
control. The CURRENT MODE indicator will come
on and output voltage will drop proportionately to
maintain constant current. In setting the CURRENT
control, allowance must be made for high peak cur¬
rent which can cause unwanted cross-over (refer to
paragraph 3-56). As discussed above, however,
if voltage is set too high with respect to current,
the supply will gross current limit and "override the
VOLTAGE setting, see paragraph 3-65.
3-10 CONSTANT CURRENT
3-11 To select a constant current output, within
the normal range ratings of the supply, proceed as
follows:
a. Short output terminals and adjust CUR¬
RENT control for desired output current.
b. Open output terminals and adjust VOLT¬
AGE controls for maximum output voltage allowable
(voltage limit) as determined by load conditions
and current selected in step (a). .If a load change
causes the voltage setting to be exceeded, the
power supply will automatically crossover to con¬
stant voltage output at the voltage setting and out¬
put current will drop proportionately. As discussed
above, however, if voltage is set too high with re¬
spect to current, the supply will gross current lim¬
it and override the VOLTAGE setting, see paragraph
3-65. In setting the voltage limit, allowance
must be made for high peak voltages which can
cause unwanted crossover (refer to paragraph 3-56).
3-12 OVERVOLTAGE CROWBAR OPERATION
3-13 Trip Point Adjustment, The crowbar trip vol¬
tage can be adjusted using the OVERVOLTAGE screw¬
driver control on the front panel. The trip voltage
range of the crowbar is approximately 0. 5 to 45Vdc
for the 6104A and 6114A supplies and 0. 5 to llOVdc
for the 6105A and 6115A supplies. To set the crow¬
bar trip voltage, perform the following procedures:
NOTE
Do not connect a load to the power
supply when setting the crowbar trip
voltage.
a. Turn OVERVOLTAGE control fully clock¬
wise and turn-on supply.
b. Set output voltage to desired trip voltage.
If the desired trip voltage is above 40 volts for the
6114A or 100 volts for the 6115A, perform the next
step. If the desired trip setting is within the max¬
imum voltage rating of the 6114A or 6115A supplies
or in order to set the trip voltage for the 6104A and
6105A supplies, go on to step (d).
c. I f the output of the 6114A or 6115A can¬
not be set to the desired crowbar trip voltage:
1. Turn off the supply.
2... Disconnect the voltage programming
pushbutton switch assembly (two wires connect
the switch assembly to Main Power Supply Board
Al).
3. Temporarily connect an external re¬
sistor (5%, 1/2W) in place of the voltage program¬
ming resistor according to the following formula:
Equt ~ * 5mA X R
Where: E out is the desired output voltage;
. 5mA is the voltage programming current; &
R is the external resistor.
For example, connect a 90Kn, 5%, 1/2W resistor if
the 6114A is to be set to 45V or a 220Kn., 5%,. 1/2W
resistor if the 6115A is to be set to 110V,
4. Turn on the supply, the output will be
the desired output voltage.
NOTE
The output voltage can be set above the
recommended ranges but the crowbar trip
voltage may not be adjustable above the
recommended ranges.
d. Slowly turn the OVERVOLTAGE control
counterclockwise until the crgwbar trips: output
falls towards 0 volt and OVERVOLTAGE indicator
comes on.
e. The crowbar remains activated and the
output shorted until the supply is turned off. To
reset the crowbar, turn the supply off. If neces¬
sary, before turning the supply back on, remove
the external resistor installed in step (c) and re¬
place the voltage programming pushbutton switch
assembly connections to the Al board. Next, set
output voltage to zero. Turn supply back on and
set it to desired output voltage (see next paragraph-
for an. important operating consideration).
3-14 False crowbar tripping must be considered
when adjusting the trip point. If the trip voltage
is set too close to the operating output voltage, a
transient in the output or load can falsely trip the
crowbar. It is recommended that the crowbar trip
voltage be set higher than the operating output
voltage by 2% + 0.’ 5V. For example, the crowbar
should be set to trip at a minimum of 31. lVdc if
the output voltage is set to 30Vdc. This operating
margin, of course, is not possible if the crowbar
is set to trip at or near its lower limit.
3-15 Resetting Crowbar. If the crowbar trips dur¬
ing normal operation (supply output goes to near
3-3

zero and OVERVOLTAGE indicator comes on), turn
Off the supply and then disconnect any load from
the power supply. Turn the supply back on and
determine if the crowbar again trips. If it does,
there is a problem in the power supply. Refer to
Section V for troubleshooting procedures that can
be used to isolate the cause of the overvoltage
condition. If the supply does not crowbar when
the load is removed, check the load circuit or the
trip point setting.
3-16 Crowbar Terminals. Terminals A13 and A14
at the rear of the supply allow the crowbar trigger
to be either monitored by an external circuit or to
be used to trip crowbar circuits in other precision
power supplies (by interconnecting the A13 and A14
terminals). If precision power supply crowbars
are to be interconnected, be sure that ail A13 term¬
inals (the positive terminal) are connected and all
A14 terminals are connected (see figures 3-9
through 3-11), The crowbar trigger pulse specifi¬
cations are given below and assume that no sup¬
plies are interconnected:
Input Trigger Pulse:
Voltage: 3V minimum, 10V maximum
Width (between 90% point at leading edge and
90%.point at falling edge): lOpsec minimum.
Output Pulse:
Voltage: 5±1V
Rise and Fall Time (between 10% and 90% points):
200nsec.
Width: 15±3 usee.
Load Impedance: lOr/min.)
3-17 CONNECTING LOAD
3-18 Each load should be connected to the power
supply output terminals (front or rear) using separ¬
ate pairs of connecting wires. This will minimize
mutual coupling effects between loads and will re¬
tain full advantage of the low output impedance of
the power supply. Each pair of connecting wires
should be as short as possible and twisted or
shielded to reduce noise pickup. (If a shielded
pair is used, connect the shield to ground at the
power supply and leave the other end unconnected.)
3-19 If load considerations require that the output
power distribution terminals be remotely located
from the power supply, then the power supply out¬
put terminals should be connected to the remote
distribution terminals via a pair of twisted or
shielded wires and each load should be separately
connected to the remote distribution terminals. For
this case, remote sensing should be used. (Refer
to paragraph 3-3 6)
3-20 Positive or negative voltages can be obtained
from the supply by grounding either one of the out¬
put terminals or one end of the load. Always use
two leads to connect the load to the supply, re¬
gardless of where the setup is grounded. This will
eliminate any possibility of output current return
paths through the power source ground. The supply
can also be operated up to 300Vdc above ground if
neither output terminal is grounded.
3-21 OPERATION BEYOND NORMAL RATED OUTPUT
3-22 The shaded area on the front panel meter
face(s) indicates the amount of output voltage or
current that may be available in excess of the nor¬
mal rated outputs (each supply is rated for two
voltage/current ranges).. Although the supply can
be operated in this shaded region without being
damaged, it cannot be guaranteed to meet all of
its performance specifications. Generally, when
operating the supply in this manner, the output is
unstable when a load is connected. However, if
the line voltage is maintained above its nominal
value, the supply will probably operate within the
specifications above the rated output. In addition,
the supply may be operated slightly above (approx¬
imately 130% at nominal line voltage) the voltage/
current range specifications (i.e. at about 1.3A up
to 40V for the 6104A/6114A or at about 0.52A up to
100V for the 6105A/6115A; or at 2A up to 26V for the
6104A/6114A or . 8A up to 65V for the 6105A/6115A),
In these operating regions, however, the supply is
in gross current limit and certain power supply
specifications (such as ripple, etc.) are degraded.
3-23 REMOTE PROGRAMMING, CONSTANT VOLTAGE
3-24 The constant voltage output of the power
supply can be programmed (controlled) from a re¬
mote location if required. Either a resistance or
voltage source can be used as the programming
device. The wires connecting the programming
terminals of the supply to the remote programming
device should be twisted or shielded to reduce
noise pickup. The front panel VOLTAGE control is
automatically disabled in the following procedures.
3-2 5 Resistance Programming (Figure 3-3). In this
mode, the output voltage will vary at a rate deter-
mlned by the programming coefficient — 2000 ohms
[ Al A2 A3 A4 A5 A6 A7 i
F
m 1
E
in 1
1
A8 +
□
F
m
R
! □
El
\-I
m
Figure 3-3. Remote Resistance Programming
(Constant Voltage)

per Volt (i.e. the output voltage will increase 1
Voit for each 2000 ohms added in series with the
programming terminals). The programming accur- .
acy is .01% of the programmed value.
3-26 The output voltage of the power supply should
be zero Volts ±1 millivolt when zero ohms is con¬
nected across the programming terminals. The out¬
put voltage may be adjusted closer to zero by ad¬
justing potentiometer A2R13 as described in para¬
graph 5-91.
3-2 7 To maintain the stability and temperature co¬
efficient of the power supply, use programming re¬
sistors that have stable, low noise, and low temp¬
erature (at least less than 5ppm per degree centi¬
grade, but preferrably 2ppm resistors) characteris¬
tics. A switch can be used in conjunction with
various resistance values in order to obtain discrete
output voltages. The switch should have make-
before-break contacts to avoid momentarily open¬
ing the programming terminals during the switching
interval.
3-28 Voltage Programming, Unity Gain (Figure 3-4),
Employ the strapping pattern shown in Figure 3-4
for voltage programming with unity gain. In this
mode, the output voltage will vary in a 1-to-l ratio
with the programming voltage (reference voltage)
and the load on the programming voltage source
will not exceed luA. Impedance matching resistor
(Rx) is required to maintain the temperature coef¬
ficient and stability specifications of the supply.
Al A2 A3 A4 A5.A6 A7
Figure 3-4. Remote Voltage Programming,
Constant Voltage
3-29 REMOTE PROGRAMMING* CONSTANT CURRENT
3-30 Either a resistance or a voltage source can
be used to control the constant current output of
the supply. The CURRENT control on the front pan¬
el is automatically disabled in the following pro¬
cedures.
3-31 Resistance Programming (Figure 3-50 In this
mode, the output current varies at a rate determined
by the programming coefficient as follows:
Model Programming Coefficient..
6104A/6114A 500 ohms/ampere
6105A/6115A 1,000 ohms/ampere
The programming accuracy is 0.25% of the program¬
med value. The output current of the supply when
zero ohms is placed across the programming term¬
inals may be set to zero by adjusting A2R12 as dis¬
cussed in paragraph 5-95.
Al A2 A3 A4 A5 A6 A7
m mi
m
la
uu \J\
PROGRAMMING
RESISTOR
A8\-t- +S -S - AI3 AI4
0 0
"Uj
W LJ
.
R i
Figure 3-5. Remote Resistance Programming,
Constant Current
3-32 Use stable, low noise, low temperature co¬
efficient (at least less than 5ppm. per degree Cen¬
tigrade, but preferrably 2ppm) programming resis¬
tors to maintain the power supply temperature co¬
efficient and stability specifications. A switch
may be used to set discrete values of output cur¬
rent. A make-before-break type of switch should
be used since the output current will exceed the
maximum rating of the power supply if the switch
contacts open during the switching interval.
--CAUTION-
If the programming terminals (A6 and +)
should open at any time during the re¬
mote resistance programming mode, the
output current will rise to a value that
may damage the power supply and/or
the load. If, in the particular program¬
ming configuration in use, there is a
chance that the terminals might become
open, it is suggested that a 1. OKn
resistor be connected across the pro¬
gramming terminals. Like the pro¬
gramming resistor, this resistor should
be a low noise, low temperature coef¬
ficient type. Note that when this re¬
sistor is used, the resistance value
actually programming the supply is the
parallel combination of the remote pro¬
gramming resistance and the resistor
across the programming terminals.
3-5

3-33 Voltage Programming (Figure 3-6). In this
mode, the output current will vary linearly with
changes in the programming voltage. The program¬
ming voltage must not exceed 1.0 volt. Voltage in
excess of 1.0 volt will result in excessive power
dissipation in the instrument and possible damage.
3-34 The output current varies at a rate determined
by the programming coefficient as follows:
Model Programming Coefficient
6104A/6114A 0.5 volts/ampere
6105A/6115A 1.0 volts/ampere
The current required from the voltage source will be
less than l(xA. Impedance matching resistor is
required to maintain the temperature coefficient and
stability specifications of the supply.
AIA2A3A4 A5 A6 A7
&
&
0
> 0 0
\-J \-J 1
R X=1K
-i- REFERENCE
"t" VOLTAGE
A8\+ + S -S - AI3 AI4
9
$
) 0
0
—~VW——*
Figure 3-6. Remote Voltage Programming,
Constant Current
3-3 5 The output current of the supply may be ad¬
justed to exactly zero when the external program¬
ming voltage is zero by adjusting resistor A2R12 as
discussed in paragraph 5-95.
3-3 6 REMOTE SENSING (Figure 3-7)
3-3 7 Remote sensing is used to maintain good reg¬
ulation at the load and reduce the degradation of
regulation which would occur due to the voltage
drop in the leads between the power supply and the
load. Remote sensing is accomplished by utilizing
the strapping pattern shown in Figure 3-7. The
power supply should be turned off before changing
strapping patterns. The leads from the sensing
(±S) terminals to the load will carry much less cur¬
rent than the load leads and it is not required that
these leads be as heavy as the load leads. How¬
ever, they must be twisted or shielded to minimize
noise pickup.
A!
a
A3 A4
0
5 A6 A7
A8 4- +S -S - AI3
AI4
?!
?n
} 0 0|
f
4
-w
Rl
Figure 3-7. Remote Sensing
3-38 For reasonable load lead lengths, remote
sensing greatly improves the performance of the
supply. However, if the load is located a con¬
siderable distance from the supply, added precau¬
tions must be observed to obtain satisfactory oper¬
ation. Notice that the voltage drop in the load
leads subtracts directly from the available output
voltage and also reduces the amplitude of the feed¬
back error signals that are developed within the
unit. Because of these factors it is recommended
that the drop in each load lead not exceed 1.0 volt.
If a larger drop must be tolerated, please consult
an HP Sales Engineer.
NOTE
Due to the voltage drop in the load
leads, it may be necessary to readjust
the constant current setting in the re¬
mote sensing'mode.
3-39 Observance of the precautions in paragraph
3-3 7 will result in a low dc output impedance at
the load. However, another factor that must be
considered is the inductance of long load leads.
This causes a high ac impedance and could affect
the stability of the feedback loop seriously enough
to cause oscillation. In this case, it is recom¬
mended that the following precautions be taken:
a. Disconnect output capacitor C12 by un¬
strapping terminal A8.
b. Connect a capacitor having similar char¬
acteristics (approximately the same capacitance,
the same voltage rating or greater, and having good
high frequency characteristics) across the load us¬
ing short leads.
3-40 Although the strapping patterns shown in
Figure 3-3 through 3-6 employ local sensing, note
that it is possible to operate a power supply simul¬
taneously in the remote sensing and constant volt¬
age/constant current remote programming modes.
3-6

3-41 SERIES OPERATION
3-42 Normal Series Connections (Figure..3-S K Two
or more power supplies can be operated in seiies to
obtain a higher voltage than that available from a
single supply. When this connection is used, the
output voltage is the sum of the voltages of the in¬
dividual supplies. Each of the individual supplies
must be adjusted in order to obtain the total output
voltage. The power supply contains a protective
diode connected internally across the output which
protects the supply if one power supply is turned
off while its series partner(s) is on.
Figure 3-8. Normal Series
3-43 AUTO-SERIES OPERATION (Figure 3-9)
3-44 Two or more power supplies can be operated
in Auto-Series to obtain a higher voltage than that
available from a single supply. When this con¬
nection is used, the output voltage of each slave
supply varies in accordance with that of the master
supply; thus the total output voltage of the com¬
bination is determined by the setting of the front
panel VOLTAGE controls on the master. The master
supply must be the most positive supply of the
series. The output CURRENT controls of all series
units are operative and the current limit is equal
to the lowest control setting. If any of the output
CURRENT controls are set too low, automatic
crossover to constant current operation will occur
and the output voltage will drop. Remote sensing
and programming can be used, though the strapping
arrangements shown in Figure 3—9 show local sens¬
ing and programming. Notice that the overvoltage
crowbar terminals (A13 and A14) are connected in
parallel which means that if any supply crowbars,
all supplies will be tripped.
3-45 In order to maintain the temperature coeffic¬
ient and stability specifications of the power supply,
the external resistors (R x ) shown in Figure 3-9
should be stable, low noise, low temperature coef¬
ficient (less than 5ppm per degree Centigrade) re¬
sistors. The value of Ry is the maximum voltage
rating of the master supply divided by the voltage
programming current of the slave supply (1/Kp
where Kp is the voltage programming coefficient).
The power rating of R^ should be at least 10 times
the actual power dissipated in the resistor. The
voltage contribution of the slave is determined by
its voltage control setting.
Figure 3-9. Auto-Series Operation,
Two and Three Units
3-7

3-46 When the center tap of an Auto-Series combin¬
ation is grounded, coordinated positive and nega¬
tive voltages result. This technique is commonly
referred to as "rubber-banding" and an external ref¬
erence source may be employed if desired. Any
change in the internal or external reference source
(e.g. drift, ripple) will cause an equal percentage
change in the outputs of both the master and slave
supplies. This feature can be of considerable use
in analogue computer and other applications, where
the load requires a positive and a negative power
supply and is less susceptible to an output voltage
change occuring simultaneously in both supplies
than to a change in either supply alone.
3-47 PARALLEL OPERATION
3-48 Normal Parallel Connections (Figure 3-10).
Two or more power supplies can be connected in
parallel to obtain a total output current greater than
that available from one power supply. The total
output current is the sum of the output currents of
the individual power supplies. The output CURRENT
controls of each power supply can be separately
set. The output voltage controls of one power sup¬
ply should be set to the desired output voltage; the
other power supply should be set for a slightly
larger output voltage. The supply set to the lower
output voltage will act as a constant voltage source;
the supply set to the higher output will act as a
constant current source, dropping its output voltage
until it equals that of the other supply. The con¬
stant voltage source will deliver only that fraction
of its total rated output current which is necessary
to fulfill the total current demand.
Figure 3-10. Normal Parallel
3-49 AUTO-PARALLEL OPERATION (Figure 3-11)
3-50 Two or more power supplies can be connect¬
ed in an Auto-Parallel arrangement to obtain an
output current greater than that available from one
supply. Auto-Parallel operation permits equal cur¬
rent sharing under all load conditions, and allows
complete control of the output current from one
master power supply. The output current of each
slave will be approximately equal to the master's
output current regardless of the load conditions.
Because the output current controls of each slave
are operative, they should be set to maximum to
prevent the slave reverting to constant current op¬
eration; this could occur if the master output cur¬
rent setting exceeded the slave's.
3-51 Additional slave supplies may be added in
parallel with the master/slave combination. All
the connections between the master and slave #1
are duplicated between slave #1 and the added
MASTER
MASTER
Figure 3-11. Auto-Parallel Operation,
Two Units and Three Units
3

slave supply. In addition, the strapping pattern
of the added slave should be the same as slave #1.
Remote sensing and programming can be used,
though the strapping arrangements shown in Figure
3-11 show local sensing and programming. In or¬
der to maintain the temperature coefficient and
stability specifications of the power supply, the
external resistors (R x ) should be stable, low noise,
low temperature coefficient (less than 5ppm per
degree Centigrade) resistors. The power rating of
Rx should be at least 10 times the actual power
dissipated in the resistor.
3-52 AUTO-TRACKING OPERATION (Figure 3-12)
3-53 The Auto-Tracking configuration is used
when several different voltages referred to a com¬
mon bus must vary in proportion to the setting of a
particular instrument (the control or master). A
fraction of the master's output voltage is fed to
the comparison amplifier of the slave supply, thus
controlling the slave's output. The master must
have the largest output voltage of any power sup¬
ply in the group. It must be the most positive
supply in the example shown in Figure 3-12.
3-54 The output voltage of the slave (Eg) is a
percentage of the master's output voltage (Ejyj),
and is determined by the voltage divider consist¬
ing of Rx and the voltage control of the slave sup¬
ply, Rp, where Eg = Ljyf |jRp/(Rx+ R^)] Remote
sensing and programming Can be used (each sup¬
ply senses at its own load), though the strapping
patterns given in Figure 3-12 show only local
sensing and programming. In order to maintain the
temperature coefficient and stability specifications
of the power supply, the external resistors (R x )
should be stable, low noise, low temperature co¬
efficient (less than 5ppm/°C) resistors. The
value of Rx is found by multiplying the voltage
programming coefficient of the slave supply by the
desired difference between the master supply volt¬
age and the slave supply voltage.
3-55 SPECIAL OPERATING CONSIDERATIONS
3-56 PULSE LOADING
3-57 When operated within either of the two range
ratings, the power supply will automatically cross
over from constant voltage to constant current op¬
eration, or the reverse, in resoonse to an increase
(over the preset limit) in the output current or volt¬
age, respectively. Although the preset limit may
be set higher than the average output current or
voltage, high peak currents or voltages (as occur
in pulse loading) may exceed the preset limit and
cause crossover to occur. If this crossover limit¬
ing is not desired, set the preset limit for the peak
rs v->/~l *-\/*vf* 1-1^0
XV. H UXiCUlOlu. UiiU UVV.
Two and Three Units
3-58 OUTPUT CAPACITANCE
3-59 An internal capacitor (C12) connected across
the output terminals of the power supply, helps to
supply high-current pulses of short duration during
constant voltage operation. To reduce current
surges, this capacitor can be removed by unstrap¬
ping terminal A 7. Any capacitance added external¬
ly will improve the pulse current capability, but
will decrease the safety provided by the constant
current circuit. A high-current pulse may damage
load components before the average regulator cur¬
rent is large enough to cause the constant current
circuit to operate.
3-60 The effects of the output capacitor during
constant current operation are as follows:
a. The output impedance of the power sup-
r»Iv ^or’vaaooG with {nc-rcia ci r\rt f rgCP 1 n f?y.
3-9

b. The recovery time of the output voltage
is longer for load resistance changes.
c. A large surge current causing a high pow¬
er dissipation in the load occurs when the load re¬
sistance is reduced rapidly.
3-61 REVERSE VOLTAGE LOADING
3-62 A diode (CR15) is connected across the output
terminals. Under normal operating conditions, the
diode is reverse biased (anode connected to the
negative terminal). If a reverse voltage is applied
to the output terminals (positive voltage applied to
the negative terminal), the diode will conduct,
shunting current across the output terminals and
limiting the voltage applied across the output ter¬
minals to the forward voltage drop of the diode.
This diode protects the series transistors and the
output electrolytic capacitors.
3-63 REVERSE CURRENT LOADING
3-64 Active loads connected to the power supply
may actually deliver a reverse current to the power
supply during a portion of its operating cycle. An
external source cannot be allowed to pump current
into the supply without loss of regulation and pos¬
sible damage to the output capacitor. To avoid
these effects, it is necessary to preload the sup¬
ply with a dummy load resistor so that the power
supply delivers current through the entire opera¬
tion cycle of the load device.
3-65 GROSS CURRENT LIMIT/AUTOMATIC DUAL¬
RANGE SWITCHING
3-66 The power supply can be operated at a CUR¬
RENT setting above the high range VOLTAGE rating
as given below:
Model
Low Range
High Range
Voltage
Current Voltage Current
6104A/6114A
6105A/6115A
0-2 0V
0-50V
0-2.0A
0-0.8A
20-40V
50-100V
0-1. 0A
0-0. 4A
For instance, the 6104A can be operated with the
CURRENT control set to 1.5A and the VOLTAGE con¬
trol set to 30V. However, as shown in Figure
3-13, if the load resistance draws output current
above the high range rating (i. e. greater than 1A
for the 6104A/6114A or 0.4A for the 6105A/6115A),
the power supply enters the gross current limit
region (the CURRENT MODE indicator comes on).
In the gross current limit region, output current is
maintained up to approximately 130% (at nominal
line voltage) of the high range rating (1.3A for the
6104A/6114A or 0. 52A for the 6105A/6115A) of the
supply while output voltage is maintained at the
VOLTAGE setting up to the maximum high range
rating. If load resistance continues to change
and causes output current to exceed the gross cur¬
rent limit region, however, the supply is automati¬
cally switched to the low range and output voltage
is reduced to approximately 130% (again, at nomin¬
al line voltage) of the low range rating (26V for the
6104A/6114A or 65V for the 6105A/6115A). Of
course, at this point the VOLTAGE setting of the
supply is overridden. Further load reductions cause
the supply to enter the constant current mode and
output voltage is further reduced as necessary to
supply the necessary output current depending upon
load requirements and the CURRENT setting. Notice
that when operated in the gross current limit region,
the supply's output is uncalibrated and may not
meet certain specifications (ripple, etc). Note,
further, that if the supply is operated at low or
high line, the gross current limit region will, vary
(decrease at low line and increase at high line).
Figure 3-13. Gross Current Limit/Dual-Range
Switching
3-10

DENOTES CONSTANT VOLTAGE FEEDBACK PATH
DENOTES CONSTANT CURRENT FEEDBACK PATH
Figure 4-1. Overall Block Diagram
4-1 OVERALL BLOCK DIAGRAM DISCUSSION
4-2 The major circuits of the power supply are
shown on the overall block diagram, Figure 4-1.
The ac line voltage is first applied to the power
transformer, after which it is rectified and filtered.
The resulting raw dc is then fed to the series reg¬
ulator, which varies its conduction to obtain the
proper output voltage or current. The series regu¬
lator includes a current limit circuit that automati¬
cally places the supply in the low voltage range
depending'upon the output voltage and current set¬
tings that have been selected and the output cur¬
rent of the supply. For instance, if the supply is
set for high voltage output and high current output
and the load attempts to draw current above the
high voltage range current specification (that is,
above 1A for the 6104A/6114A supplies or above
0.4A fox the 6105A/6115A supplies), the series
regulator limits the output current and then de¬
creases the output voltage to the low range. When
in the low range, the output current is then allowed
to reach the CURRENT setting up to the maximum
rating of the supply. Notice, further, that dual
rectifier-filter circuits are employed to provide a
low value of raw dc voltage to the series regulator
in order to minimize internal power consumption
during low voltage (high current) operation. Each
rectifier-filter furnishes most of the raw dc voltage
to the regulator during one of the two output voltage/
current ranges of the supply.
4-3 The series regulator is part of a feedback
loop consisting of the driver and the constant vol¬
tage/constant current comparators. When operated
within the specified ranges, during constant voltage
4-1

operation the constant voltage comparator contin¬
uously compares the output voltage of the supply
with the drop across the VOLTAGE control. If these
voltages are not equal, the comparator produces an
amplified error signal which is further amplified by
the driver and then fed back to the series regulator
in the correct phase and amplitude to counteract
the difference. In this manner, the constant vol¬
tage comparator helps to maintain a constant out¬
put voltage and also generates the error signal
necessary to set the output voltage at the level
established by the VOLTAGE controls.
4-4 During constant current operation, the con¬
stant current comparator detects any difference be¬
tween the voltage drop developed by the load cur¬
rent flowing through the current sampling resistor
and the voltage across the CURRENT control. If
the two inputs to the comparator are momentarily
unequal, an error signal is generated which (after
amplification) alters the conduction of the series
regulator by the amount necessary to reduce the
error voltage at the comparator input to zero.
Hence, the IR drop across the current sampling re¬
sistor, and therefore the output current, is main¬
tained at a constant value.
4-5 The constant voltage comparator, then, tends
to achieve zero output impedance by altering the
output current whenever the load resistance
changes. Conversely, the constant current com¬
parator attempts to achieve infinite output imped¬
ance by changing the output voltage in response to
any load resistance changes. Thus, it is obvious
that the two comparison amplifiers cannot operate
simultaneously. When the supply is operated
within the two normal ranges of output voltage/
current, it must act either as a constant voltage
source or as a constant current source - it cannot
be both. Further, as previously mentioned, if the
supply is set to operate outside of the specified
high voltage range current rating (i.e. both VOL¬
TAGE and CURRENT are set to high values), the
supply will enter the current mode and limit output
current if the load resistance attempts to draw more
than one-half of the maximum current rating of the
supply. As it limits output current, the supply
also lowers output voltage (overriding the VOLTAGE
setting) until the low voltage range is reached. At
this point, the supply enters the constant current
mode in which the output current is maintained
(up to the maximum rating of the supply) at the
CURRENT setting by altering the output voltage.
4-6 Figure 4-2 shows the output characteristics
of a constant voltage/constant current power sup¬
ply. When operated within either of the two nor¬
mal output voltage/current ranges (0-40V up to
1A or 0-20V up to 2A for the 6104A/6114A supplies
or 0-100V up to . 4A or 0-50V up to . 8A for the
6105A/6115A supplies). With no load attached
(Rl=co), Iqut= 0, and Equt = Eg, the front panel
voltage control setting. When a load resistance is
applied to the output terminals of the power supply,
the output current increases, while the output vol¬
tage remains constant; point D thus represents a
typical constant voltage operating point. Further
decreases in load resistance are accompanied by
further increases in Iqut with no change in the
output voltage until the output current reaches Ig,
a value equal to the front panel current control set¬
ting. At this point the supply automatically changes
its mode of operation and becomes a constant cur¬
rent source; still further decreases in the value of
load resistance are accompanied by a drop in the
supply output voltage with no accompanying change
in the output current value. With a short circuit
across the output load terminals, Iqut * l S and
Equt = 0*
Figure 4-2. Operating Locus of a CV/CC Supply-
Operated Within Range Ratings
4-7 Thus, at VOLTAGE and CURRENT settings
within the two normal ranges, the •’crossover" val¬
ue of load resistance can be defined as Rq= E§/lg.
Adjustment of the front panel VOLTAGE and CURRENT
controls permits this "crossover" resistance to
be set to any desired value from 0 to CO. if Rl is
greater than R c , the supply is in constant voltage
operation, while if is less than Rq, the supply
is in constant current operation.
4-8 Figure 4-3 shows the output characteristics
of the supply when it is operated at an output cur¬
rent setting above the high voltage range rating